Reciprocating power hammers are either of the double air cushion or spring design or single air cushion design. The former type of tool is described in U.S. Pat. No. 1,191,948 and German Pat. No. 255,977 issued in 1918 to Heinrich Christiansen. Pertinent single air spring designs are described in U.S. Pat. No. 2,880,585 and U.S. Pat. No. 3,688,848, assigned to The Black and Decker Manufacturing Company, the assignee herein.
The double air spring device as understood by the inventors herein, does not afford an idling arrangement when the tool is disengaged from the work surface or when the tool bit is removed from the unit. In the aforementioned single air spring designs relatively intricate air transfer systems are described for accomplishing air replenishing and idling. These necessitate the machining of the piston and surrounding guide tube to provide appropriate grooves and annular cut outs to effect the required air transfer.
The fact that these prior art systems require that the piston and guide tube employ grooved surfaces, results in reduced reliability in that excessive wear results, for example, on the piston sealing ring which is continually reciprocated past the grooves cut in the guide tube.
Further, because of the need to machine these surfaces so as to provide this intricate grooving, the thickness of the starting material for the piston and the guide tube must be sufficiently adequate to allow for the cutting of the grooves. Further, the material for the piston, guide tube and ram must be sufficiently hard so as to provide long wear and thus extend the reliability of the unit. For example, the design of the '848 patent employed steel for the piston and tube members. The heavier the material used in this air unit, the greater the vibrational effects resulting from the continuous reciprocation of the piston and the striking of the ram against the tool bit.
Further, in the '848 patent, for example, the ram or striker is typically an intricately machined part. This is so because it is one of the cooperating members in the air transfer system.
It is therefore a primary object of this invention to provide an improved air replenishing and idling system which employs easily machined, cooperating parts.
It is yet another object of this invention to employ lighter weight material so as to reduce the shock and vibration experienced by the operator.
It is still another object of this invention to provide an air transfer system which allows for easy achievement of an idle mode when the tool bit is removed or the mechanism lifted off the surface being worked.